The invention relates to a method and an apparatus for transporting a payload in a synchronous information transmission network in the form of concatenated virtual containers.
In a synchronous information transmission network that operates according to the ITU-T recommendations for synchronous digital hierarchy (SDH) or for Synchronous Optical Network (SONET), payload signals are transmitted within a frame structure, whose frames are referred to as synchronous transport modules. The basic unit is the STM-1 transport module. Larger transport modules of the STM-4, STM-16 or STM-64 type are created by nesting the bytes of several (4, 16 or 64) STM-1. The transport modules contain one or several virtual containers, which contain the payload to be transported. The largest virtual container with a transmission capacity of 145 Mbit/sec is the VC-4. A payload that is larger than the capacity of the VC-4 can be transmitted in the form of linked or concatenated containers. This means that the payload signal is divided into blocks, each of which is transported in a VC-4, and that the concatenation guarantees that the blocks at the other end of the transport network can be reassembled into their original sequence with the correct phase relationship .
There are two forms of concatenation, namely virtual concatenation and contiguous concatenation. The two forms should furthermore be capable of being converted one into the other. The present invention primarily relates to the first form of concatenation, virtual concatenation, but also relates to how the two forms of concatenation can be advantageously converted one into the other. In contiguous concatenation, the concatenated containers are transmitted as a unit in a relatively large transport module, for example STM-4, and only the path overhead of the first of the concatenated VCs is evaluated. In virtual concatenation the concatenated containers are transmitted independent of one another and are not reassembled into the original phase relationship and sequence until the end of the transmission path. Usually, concatenation is first created based on contiguous concatenation and then transformed into a concatenation based on virtual concatenation.
The prior art proposals provide that all functions of the virtual concatenation be administered by a management system (xe2x80x9cnetwork managerxe2x80x9d). A further proposal provides that the virtual containers contain an identifier called the TTI (Trail Trace Identifier). This identifier is contained in the JI-byte of the path overhead in each virtual container, indicates the source of the respective virtual container, and is normally assigned by the network management system. According to this further proposal, all virtual containers that are concatenated by means of virtual concatenation should receive the same identifier. However, in previous practice all virtual containers have received different identifiers. Prior art solutions proposed for the concatenation of virtual containers have the following disadvantages:
The number of concatenated containers cannot be changed during a connection, since the change in the number of concatenated containers would have to take place synchronously in all network nodes. The network manager does not guarantee this a priori.
The sequence in which the containers are transmitted in the multiplex structure must be administered.
The identification of the individual containers within a concatenation is not precisely described.
If containers arrive in the wrong sequence, misleading alarms are produced according to prior art specifications.
Today""s network management systems are not prepared to properly handle several containers with identical TTIs.
The object of the present invention is to present a method for transmitting a payload in the form of concatenated containers, which can be used variably and which overcomes the disadvantages of prior art solutions. In particular, it is the object of the present invention to present a method in which the number of concatenated containers can be changed during transmission. A further object is to present a network element to implement this method.
In terms of the method this object is attained by the features of Claim 1 and in terms of the network element by the features of Claim 10. Advantageous embodiments are presented in the dependent claims.
The present invention has the following advantages:
A virtual concatenation does not require management of variable capacity for the duration of a connection.
The virtual containers can be transmitted in the multiplex structure (STM-N) in any sequence. According to the method proposed in the present invention, the containers are automatically resorted at the other end of the transmission path.
Only those network nodes in which a conversion from virtual concatenation to contiguous concatenation and vice versa takes place have to be retrofitted.
All of the virtual containers (VC) belonging to a virtual concatenation can be unambiguously identified.
A plurality of virtual containers can be transmitted within a multiplex structure (STM-N) without the risk of confusing the virtual containers.